1. Field of the Invention
The present invention relates to a method of conducting a modal mass analysis for measuring a quantity of each specified ingredient gas among ingredient gases to be measured such as CO, CO.sub.2, NO.sub.x, HC and the like, in an exhaust gas from a motor vehicle for various modes of driving (idling, accelerating, constant-speed driving and decelerating), and in particular, to a method of conducting a modal mass analysis of an exhaust gas from a motor vehicle on the basis of a procedure that a flow rate Q.sub.E (t) of the exhaust gas exhausted from a motor vehicle tested in a driving simulation having an appointed driving-mode change-over sequence, is measured in an appointed sampling time period and a concentration C.sub.E (t) of an ingredient gas to be measured in the exhaust gas is measured in the same sampling time period as in the measurement of said flow rate Q.sub.E (t) of the exhaust gas, and then a quantity M(t) of the ingredient gas in the exhaust gas is determined for each driving mode by the use of the following equation (2): EQU M(t)=.rho..times.C.sub.E (t).times.Q.sub.E (t) (2)
wherein .rho. is a density of the ingredient gas to be measured.
2. Prior Art
Many prior methods are well known for such a method of conducting a modal mass analysis of an exhaust gas from a motor vehicle. In one such method, a dilute stream method, a flow rate (constant for each system) of a diluted exhaust gas is used as the flow rate Q.sub.E (t) in equation (2) and a measured result of a concentration of an ingredient gas in the diluted exhaust gas is used as the concentration C.sub.E (t) in equation (2).
In a second prior method, a CO.sub.2 -tracing method, the flow rate Q.sub.E (t) in equation (2) is determined by comparing the result of a measurement of the concentration of CO.sub.2 in a raw (undiluted) exhaust gas with the measured concentration of CO.sub.2 in the exhaust gas after the exhaust gas has been diluted, and the result of a measurement of concentration of an ingredient gas in the raw exhaust gas is used as the concentration C.sub.E (t) in equation (2).
In a third method, a dilution air quantity method, the flow rate Q.sub.E (t) in said equation (2) is determined as a difference between a flow rate (constant for each system) of the diluted exhaust gas and a measured dilution air quantity, and a measured concentration of the ingredient gas in the raw exhaust gas is used as the concentration C.sub.E (t) in equation (2).
However, in every case both the measurement of the flow rate Q.sub.E (t) of the exhaust gas and the measurement of the concentration for determining the concentration C.sub.E (t) of the ingredient have been carried out without a substantial delay relative to a point in time of change in driving mode and in an appointed common sampling time.
However, the above described conventional methods have shown the following vital disadvantages:
Referring to FIG. 4, there is shown a timing chart schematically showing representative changes in exhaust gas flow (Q.sub.E) and exhaust gas ingredient concentrations (C.sub.E) from a motor vehicle on a real time basis for different driving modes, in which IDL indicates an idling driving mode, ACC indicates an accelerating driving mode, CRU indicates a constant-speed driving mode and DEC indicates a decelerating driving mode, the driving modes being changed over on the basis of an appointed sequence. As is apparent from this chart, the flow rate Q.sub.E (t) of the exhaust gas is changed following each driving mode changes at times H.sub.1, H.sub.2, H.sub.3, H.sub.4 nearly without any delay, while the concentration C.sub.E (t) of the ingredient gas is changed respectively following certain delay times .tau..sub.1, .tau..sub.2, .tau..sub.3, .tau..sub.4 relative to the respective change-over times H.sub.1, H.sub.2, H.sub.3, H.sub.4, due to a delay in response incidental to a piping system and a gas-concentration analyzer, absorption and desorption phenomena of ingredient gases to be measured and the like. In addition, since each of said delay times .tau..sub.1, .tau..sub.2, .tau..sub.3, .tau..sub.4 is difference for each of the driving mode changes and each of the ingredients to be measured, the data of said concentration C.sub.E (t) of the ingredient gas put out from the gas concentration analyzer in real time have a form enlarged or compressed relatively to a time axis in each driving mode.
However, even though such a changing state of data is realistic, it has been quite disregarded in the prior methods. For example, both the measurement of the flow rate Q.sub.E (t) of the exhaust gas and the measurement of the concentration C.sub.E (t) of the ingredient gas have been carried out at equal time increments in a manner as shown by marks .circle. in FIG. 5 (illustrating a case of the accelerating driving mode ACC). In short, as above described, both the measurement of the flow rate Q.sub.E (t) of the exhaust gas and the measurement of the concentration C.sub.E (t) of the ingredient gas have been carried out substantially without any delay relative to the points in time of changing over the driving mode, so that in each driving mode the sampling data of the concentration C.sub.E (t) of an ingredient gas corresponding to other driving modes are mixed and sampling data of the flow rate Q.sub.E (t) of the exhaust gas do not correspond to the sampling data of the concentration C.sub.E (t) at a ratio of 1:1 in phase, and number. Accordingly, even in a case of an average value method, in which an average quantity M of an ingredient gas is determined for each driving mode, a disadvantage has occurred in that an error of 20 to 30% is produced. In addition, in a case of an instantaneous operational method, in which a quantity M(t) of an exhaust ingredient gas is measured and determined following successive time increments, the error in M(t) is too large to be accepted.
However, recently required improvements in the performance of motor vehicles in view of governmental regulations of exhaust gas emissions, fuel-use efficiency and the like have been increasingly tightened up. In this sense, it has been eagerly desired to turn the instantaneous operational method, which is capable of investigating exhaust gas emission in greater detail to practical use (by improving its accuracy and simplifying its implementation).